A three year longitudinal clinical trial of MFP-NaF dentifrice formulated at different fluoride concentrations. The purposes of this procurement are: to evaluate the anticaries efficacy of a combined MFP-NaF dentifrice with a total fluoride concentration of 1000 ppm; and to determine whether the efficacy of this formulation can be improved by raising the total fluoride concentration to 2500 ppm. A standard MFP dentifrice with a fluoride concentration of 1000 ppm will be used as a positive control. Both experimental formulations will contain NaF and MFP at concentrations equimolar with respect to fluoride.